This invention relates to a color image processing method and a color image processing apparatus.
In recent years, development of print systems have been in progress, and it has been put into practice to use a system in which an image on a film is read by a scanner and the image is converted into image data, by the use of which an image is printed after image processing by a printer. A system of such a type is called a mini-laboratory. A system of such a type is based on a film (a negative film), and is made up according to a way of thinking which is the same as conventional photography without a colorimetric concept. That is, a dye quantity space is used.
For the purpose of actualizing this system, it is used a method in which inputted image data are transformed into data in density region (dye quantity region) by a tone transform, and printing is done after a matrix transform and the modification of tone. FIG. 9 shows the concept of a conventional system. The system shown in the drawing is such that R, G, and B signals are inputted as scanner signals, and after the respective tone transforms, C, M, and Y printer signals are produced.
In the drawing, 1 denotes a tone transform section for inputting data of red (R) out of image data obtained by the scanning of a film by a scanner and practicing tone transform, 2 denotes a tone transform section for inputting data of green (G) out of the scanner signals and practicing tone transform in the same way, and 3 denotes a tone transform section for inputting data of blue (B) out of the scanner signals and practicing tone transform in the same way.
Further, 4 denotes a matrix transform section for receiving output signals of these tone transform sections 1 to 3 and practicing matrix transform, 5 denotes a tone transform section for receiving an output signal of said matrix transform section 4 and practicing tone transform to output a signal of cyan (C), 6 denotes a tone transform section for receiving another output signal of said matrix transform section 4 and practicing tone transform to output a signal of magenta (M), and 7 denotes a tone transform section for receiving another output signal of said matrix transform section 4 and practicing tone transform to output a signal of yellow (Y).
To explain the operation of the system having such a structure, it will be as follows.
The scanner (not shown in the drawing) scans a negative film (not shown in the drawing) to output scanner signals R, G, and B. These scanner signals R, G, and B are inputted to the respective tone transform sections 1 to 3, undergo tone transform, and are transformed into signals representing density (dye quantity). The image signals, after transformed, are inputted to the matrix transform section 4, and are subjected to matrix transform. The signals, after subjected to matrix transform, are inputted to the respective tone transform sections 5 to 7, and are subjected to tone transform, to be outputted as printer signals C, M, and Y for a printer. The printer (not shown in the drawing) prints a color image on the basis of these printer signals.
On the other hand, there is a requirement to write digital signals generated in the process of a signal processing in an electronic medium such as a CD-R and to appreciate the image on a display. In the case where certain image data are once written in an electronic medium, and an image is printed from the electronic medium, there is an advantage that the same color reproduction as in the case of an image directly printed from a negative film can be obtained.
However, at the same time, it is necessary that the digital signals present a correct appearance when the image is displayed on a display. In “A. Yoda et al, ‘Color Image Processing in Fujifilm's Digital Imaging Servers’, IS & T's PICS Conference (2001)”, it is shown to make a color transform with a reference printer taken for the reference.
In a method using dye quantity, owing to no calorimetric reference being present, when it is intended to display an image on another medium such as a CRT or a liquid crystal display, a correct color reproduction is not made in some cases. For example, there is a problem that the color of an image as printed is not reproduced on a display such as a CRT, in the case where signals to be transmitted to a printer are directly recorded in a CD-R as they are.
Further, there has been also a problem that, in the case where an image was printed from a medium in which the image data were recorded, for example, in the case where the data were recorded in such a way that a correct color was presented when the image was displayed on a display of the sRGB standard (specified in the standard RGB Standard: IEC 61966-2-1), printing by the use of this system could not be done appropriately.
In the example of the above-mentioned reference, even in the case of direct printing, a two-time process, that is, a print scanner→a reference printer, and the reference printer→a printer, is required, and as regards a method of preparing the inverse (YMCK→RGB) LUT, it is made only a description to the effect that an inverse color gamut mapping is carried out. For this reason, the calculation load was heavy, and for the preparation of the inverse LUT, it was necessary every time to carry out a transform into a uniform color space and color gamut mapping in it. Owing to this color gamut mapping, there has been a problem that the working time of operation was increased, and an error was produced in the process of the inverse transform.
This invention was made in view of the above-mentioned problems, and it is its object to provide such an image processing method and an image processing apparatus as to make a printed color approximately the same as a color represented on a display in the case where a negative film is read by a scanner. Further, it is another object of the invention to provide an image processing method and an image processing apparatus capable of carrying out the calculation correctly and easily, for LUT's in the inverse relationship with each other used in this method. A further object of this invention is to provide an image processing method and an image processing apparatus not requiring two-time color gamut mapping and being capable of processing data by an inverse operation only, hence having no problem accompanied by the above-mentioned color gamut mapping. Further, it is another object of the invention to provide an image processing method and an image processing apparatus capable of making it possible to easily apply an optimized color transform to image data, in the case where the image data are not those which have not been recorded by this system.